6V6 Tube Advice for 5F1?

Discussion in 'Shock Brother's DIY Amps' started by PorkChopExpress, Jun 27, 2020.

  1. Lowerleftcoast

    Lowerleftcoast Tele-Afflicted

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    I agree with Nickfl. A different tube would be the easiest way for a win win.

    @elpico suggested a bucking transformer which is a handy device to have around when powering tube amps with modern wall voltages . It may get the amp in a zone where the Tung Sol can be happy. On the other hand, IMO, this 5F1 has voltages I can live with. The heaters are ~6.7VAC. The B+ is ~372VDC. (It is just the Tung Sol that can't live with it.)

    I happen to like the new Tung Sol and I might just want to adjust the amp to keep it from red plating. I don't often disagree with elpico but this time I'll go out on a limb. Since your Cathode Resistor measured at 460 ohms, you can replace it. It may be a bandaid to get this Tung Sol in check but changing the cathode resistor a handful of ohms up or down IMO will not *bias it off center*. (IMO, the bias is too hot for the Tung Sol and too cool for the JJ.)
     
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  2. PorkChopExpress

    PorkChopExpress TDPRI Member

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    Thank you all for the great feedback on this. I’d really like to find a way to get that Tung Sol tube to work since the sound was spot on IMHO.

    The bucking transformer is something I’d love to have on hand and seems fairly cheap to put together - thank you @elpico for the design info.

    One last question: What if I put a resistor between the rectifier and first filter cap to reduce the overall voltage to the circuit? Could that result in a cool enough bias for the Tung Sol to be happy? Has anyone done this?
     
  3. jsnwhite619

    jsnwhite619 Friend of Leo's

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    What brand rectifier are you currently using? I think JJ's typically drop more voltage among new production 5y3's. However, your voltages are basically what I would expect to see with the PT. I've used it before and I think it was around 380v B+. I guess you just have to decide how much you want to tweak things to use THAT tube.

    EDIT:. Went back through things here. I use a 500R cathode resistor on my 5f1/5f2a builds and Mojotone sends their kits with a 500R cathode resistor. If yours is spec'd lower than stock already. I'd get on eBay or Amazon, order a 500R resistor to replace that one, and your problems will likely be solved.

    Sent from my moto g(6) using Tapatalk
     
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  4. Wally

    Wally Telefied Ad Free Member

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    First of all, I do not put any stock at all in the specs for the Russian Tung Sol 6V6. The spec sheet that comes up for it is simply a spec sheet from the original Tung Sol company. For that and other reasons, I don’t use that tube. Also, at some point I the late ‘50s iirc the max plate dissipation for US 6V6s was changed to 14 watts...same tubes as those that earlier had a rating of 12 watts. If one uses 12 watts, one will be safer, I suppose...especially in fixed biased amps.
    Secondly, that is not uncommonly high plate dissipation for any Fender Champ amp, ime. Techs for decades have witnessed 16-18 watts of plate dissipation as more of a norm than not. I had a 1971 SF Champ, which was the best sounding BF/SF ?Champ I have ever been around, which was running almost 150% of plate dissipation with the original 6V6 in it.....45 years down the line. My friends BF Champ was running 18 watts at the same time....we had to know due to the difference in the Sonics. His amp was wonderful....mine was beyond that. His eyes went wide when he heard it.
    So, I don’t know why that Tung Sol ‘Reissue’ is redplating, but I personally would not waste time on it except as a learning experience. It might be interesting to see at what plate dissipation point the redplating went away. After I learned that, I would be through with it unless by some strange happenstance it had some sort of interesting Sonic.

    just a comment about your voltage chart. It is of no major importance since obviously you did get the proper measurements for the AC high voltage secondary, but fwiw those pins are pins 4 and 6 rather than 3 and 5.
     
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  5. PorkChopExpress

    PorkChopExpress TDPRI Member

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    Thanks for the correction, I’ll edit my voltage chart post to avoid future confusion. I must have gotten my wires crossed (in my brain, not the amp).

    Also, this is good to know - I wasn’t sure what to make of the spec sheet for the Tung Sol. I like the way it sounds running hot and wouldn’t be changing a thing if it wasn’t red plating.
     
  6. PorkChopExpress

    PorkChopExpress TDPRI Member

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    It is in fact a JJ 5Y3S - I’m glad to know that my voltage readings are in the ballpark though.

    Dave from Boothill offered to sell me an older, more tried and true rectifier tube to help level things out. I guess that’s an option as well.
     
  7. VintageSG

    VintageSG Friend of Leo's Ad Free Member

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    You can find NOS JAN Sylvania VT-107 6v6 valves from the 1940's for less than the price of new production if you're patient. There were squillions produced for the war effort and they crop up regularly.

    The JJ 6V6S is about as tough as they come, and they sound OK in simple, single ended amps, but OK isn't good enough. I'm not keen on them in my Champ-a-likes, as I've heard much better from the aforementioned JAN valves and the Soviet 6p6s, a 6V6 analogue. The 6p6s is as cheap as chips, sounds more than fine, being as it's a 1:1 of an American valve, that's no surprise, but they may have a surprise in store if they're run too hot. Note the JJ sounds quite wonderful in push-pull amps, and is near indestructible.

    Hunt down some NOS examples, maybe a few 6p6s too, try them, measure them, mark the boxes. Whatever doesn't 'plate and tickles your ears is fine. Don't worry too much about being over 100% It bugged me at first, I checked the measurements, checked the math, then I learned to relax and love the sounds. If a valve is running safely, and sounds glorious, it's the right valve in that amp.
     
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  8. corliss1

    corliss1 Friend of Leo's Platinum Supporter

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    Of all the tubes in the world that get NOS hype, I usually don't buy it. But I do always get NOS 5y3 tubes because they last forever and are still pretty cheap.
     
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  9. elpico

    elpico Tele-Holic

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    While 6.7Vac on the heaters may be technically "in spec" according to the sheet it's not a situation where any number between 5.7 and 6.9 has the same outcome. Running them at the high end of the range like that can reduce average tube life by 50% compared to running them at the low end of the spec. I guess that much variation sounded fine to the people selling the tubes in those days, but I'd think whether it really is fine is up to the one buying the tubes. Personally I always aim to keep it around 6V, which to me makes this amp a good candidate for an overall voltage reduction, but only you know whether it matters in your house.

    FWIW 6.7V heaters and 375V B+ is not what champs were supposed to run at or what I would call "normal". They're running out of spec now for the reason described in RG Keen's page, the wall voltage has gone up 10% since the amps were built. We know what the normal voltages were for the 5F1 because Leo included them on the layout drawing:

    [​IMG]

    My eyes might not be the best but I'm pretty sure that says the B+ is supposed to be 340Vdc.
     
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  10. jsnwhite619

    jsnwhite619 Friend of Leo's

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    Hammond's 275v secondary transformers nails those voltages across the board with JJ's.

    Sent from my moto g(6) using Tapatalk
     
  11. bieworm

    bieworm TDPRI Member

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    No not a resistor... it will sag too much. Just try a couple of 5W zener diodes in series just before the first filter cap. Make sure you orientate them right...it will help to drop the B+ in theory the voltage drop is the same as the zener diode value. So a 10V zener will drop 10V on the B+. But due to heat generation you'd be better off with multiple 5V/5W zeners in series.
    Cheapest, easiest and most safe way to drop that B+. Tried and tested..
     
  12. King Fan

    King Fan Poster Extraordinaire

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    I gotta side with @elpico here (an easy choice, since I've only ever seen him give good advice). If this is my amp, I want to address the root problem of high B+.

    Rob talks about a *lot* of ways to drop B+ on his 5E3 mods page -- equally relevant in the 5F1. As mentioned above, the simplest win-win method is to use a vintage 5Y3 -- they typically drop more voltage than any modern version (and a *lot* more than Sovtek) -- and sound better.

    At the other end of the scale, also as above, a better-spec PT is a cool and elegant solution. But then there's the expense... and a lot of unsoldering...

    Let me give the bucking transformer a big thumbs up. For about $50 in parts, mine made *all* my tweed amps sound (and measure) *way* better, and with the side-benefit of heater voltages that will keep my nicer tubes living a long time.

    Finally, although zeners (often mounted on the PT CT for cathode bias) are very popular, I wouldn't overlook a simple dropping resistor. Sag and bloom sound great in a Champ, IME, and if a 5F1 draws, what, maybe 40mA of B+, a 470 or 500 ohm wire wound between rectifier and first filter cap might drop your B+ by about 20V. Trust me, it's simple and works well -- I did it in my VibroChamp and it sounds great.
     
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  13. jsnwhite619

    jsnwhite619 Friend of Leo's

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    Since 370v B+ isn't that high, and the tube is obviously biased too hot, is it worth building a bucking transformer that you always have to take with you and rely on vs just increasing the bias resistor to 500R since it's already valued lower than it should be? $6-8 online can probably get you 5 resistors to measure and choose from.
     
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  14. jman72

    jman72 Tele-Afflicted

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    I feel your pain, but don't have the answer. I put a set of Tung Sols in my 5e3 build a few years back and they sounded great...for five minutes until they red plated. That was with a larger value bias resistor. I switched to JJs and never looked back. I don't really stress about small changes in perceived tone from the tubes since I like to use several ODs to get my drive and some other pedals, too. The ruggedness of the JJs works for me.

    I also just put a JJ in a 5f1 build and it sounds pretty good. I'd like to try a different 6v6, but I know that these amps run hot and I don't want to spend a lot on a NOS tube.
     
  15. PorkChopExpress

    PorkChopExpress TDPRI Member

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    I really appreciate all this advice. I’m blown away by all of your thoughtful responses to my rookie level questions. I have a lot of options to consider and will probably do some experimenting to figure out what works best. I’ll likely start with a vintage 5Y3 and see what happens to the voltage. Maybe grab a few resistors to play around with if that doesn’t do the trick.

    I’ll post an update to this thread with the results. What a great forum. Thanks again!
     
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